This invention relates generally to electrostatic reproduction apparatus and in particular to the removal of the residual toner particles from a photoconductive element after a transfer operation.
In order to remove residual toner from a photoconductive surface, it is usually necessary to dissipate the electrostatic image on the drum which strongly binds the residual toner to the drum surface. For this reason a corona discharge unit is often used to apply an electric field opposite in polarity to the initial electrostatic charge to neutralize the electrostatic image on the drum, and to use a light source to subsequently illuminate the drum surface to cause further discharge of the drum. For example, Japanese publication 38-12993 shows illumination from behind the photoreceptor over the entire area of image transfer and cleaning to discharge the photoreceptor and to facilitate both transfer and cleaning. U.S. Pat. No. 3,838,921 shows illumination both behind and in front of a photoreceptor belt to discharge the belt and facilitate cleaning when the system is on a cleaning cycle. U.S. Pat. No. 4,201,465 discloses illumination between the preclean corona and the cleaning station when the system is on a cleaning revolution. U.S. Pat. No. 4,205,912 shows an illumination source to discharge the photoreceptor prior to cleaning during a cleaning revolution, and also shows an illumination source just after the cleaning station to condition the photoreceptor prior to charging for the next exposure.
A difficulty with the above described systems is that they are either used in a two-cycle xerographic system and are not adapted to one cycle system operation. It is also known to discharge the photoreceptor via light after the preclean station in order that the voltage variation of the photoreceptor entering the cleaner can be minimized. Since cleaning is primarily a field driven process with certain types of cleaners, control of the incoming photoreceptor potential enhances cleaning latitude. With light at the cleaning nip region, the charge is eliminated from the photoreceptor, and the toner tends to be attracted to the negatively charged magnetic brush, after a positive charge from the preclean corotron changes the negative charged toner to a positive charge. A difficulty with this type of system is that an electrostatic field remains at the exit of the cleaning nip and there is a tendency for the redeposition of toner onto the surface of the photoreceptor from the cleaning brush. A difficulty with the above systems, also, is that there is still an appreciable amount of degradation of the belt and a buildup of toner on the belt as well as bead loss from the magnetic brush causing spots on the copies.
It is an object of the present invention, therefore, to provide a new and improved single cycle cleaning system that provides less degradation of the belt and a less likely buildup of toner on the belt and bead loss from the magnetic brush. It is another object of the present invention to broaden the redeposition failure limit resulting in improved cleaning latitude.
Further advantages of the present invention will become apparent as the following description proceeds and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.
Briefly, the present invention is a cleaning system in which the cleaning nip region is kept dark and light is projected between the preclean corotron and the nip of the magnetic cleaning brush and also light is projected at the exit of the cleaning nip region prior to the charge corotron. Cleaning occurs at the entrance of the nip, and as the photoreceptor moves through the cleaner nip, it is charged in the direction that the cleaning roll is biased. This reduces the electrostatic field at the exit of the cleaning nip and, in turn, minimizes the redeposition of wrong sign toner onto the photoreceptor as well as reducing field driven bead loss, that is the difference in voltage between the mag brush cleaner and the photorecptor.